As most electronic equipment including personal computers, digital cameras and mobile phones become of smaller size and better performance, there is an increasing demand for semiconductor devices of small size, thin profile and high density. There is a desire to have a photosensitive dielectric material which can accommodate an increase of substrate area for productivity improvement and which can accommodate structures having fine asperities with a high aspect ratio on substrates in the high-density packaging technology as typified by chip size packages or chip scale packages (CSP) or 3D layer stacks.
Recently, in the high-density packaging technology as typified by CSP or 3D stacked packages, a focus is put on the technique of redistribution from chips by forming a fine, high aspect ratio pattern on a substrate and depositing a metal such as copper on the pattern. To meet a demand for chips of higher density and higher integration, it is strongly desired in the redistribution technology to reduce the width of pattern lines and the size of contact holes for interconnection between substrates. The lithography is generally used for forming fine size patterns. In particular, the lithography combined with chemically amplified negative tone resist compositions is suited for forming fine pattern features. Since the pattern used for redistribution is permanently left between device chips, the pattern-forming material must have a cure ability and also serve as an electric/electronic part-protecting film having flexibility, heat resistance, electric properties, adhesion, reliability and chemical resistance. For this reason, a negative resist composition is believed suitable for forming such patterns.
Accordingly, a chemically amplified negative resist composition is typical of the pattern-forming material which can be processed into a fine redistribution layer and serve as an electric/electronic part-protecting film having flexibility, heat resistance, electric properties, adhesion, reliability and chemical resistance.
On the other hand, for the negative resist material in current use, it is desired to develop a material in which an opening profile is controlled in order to process a fine redistribution layer. Since the exposure dose for pattern formation increases with an increase of film thickness, the efficiency of acid generation of the photoacid generator in a surface layer relative to exposure is relatively high as compared with that in a bottom layer relative to exposure, suggesting that the profile of openings in the pattern surface layer is liable to assume T-top shape. If the T-top shape is included, they cause failures such as defects during coating formation by the subsequent redistribution processing step and cracks generated in the pattern in various environmental load tests. The cause of T-topping is that on use of a chemically amplified negative resist material, a pattern is formed by crosslinking by the acid generated upon exposure. The problem may be solved if an appropriate amount of basic component is available in the surface layer during pattern formation. The solution is difficult because even when a basic compound coexists in a composition, it is impossible to localize the basic compound in the surface layer.